# Homework Help: Sunlight Intensity

1. Mar 21, 2006

### 1ceHacka

I need help with this problem...

Suppose that the intensity of the sunlight that reaches Earth's upper atmosphere is approximately 1200 W/m2. Earth is about 1.5 times 108 km from the Sun.

What is the total average power output of the Sun, assuming it to be an isotropic source?

2. Mar 21, 2006

### Hootenanny

Staff Emeritus
Do you have any initial thoughts and/or working?

3. Mar 21, 2006

### 1ceHacka

I know that average power is related to the intensity and the surface area.

4. Mar 21, 2006

### Staff: Mentor

You need to start with the correct distance of the Earth from the sun (definitely not "1.5 times 108km from the Sun"), and that will give you the surface area of a sphere at the Earth's radius from the Sun. Since you are given the power density at that radius, you should be able to calculate the total power flux through the whole sphere at that radius. Given that number, what is the total power flux at other radius values?